Question

想象一对一对多的关系，例如：

Mail: subject, date etc 
Recipient: address

是否可以执行此查询不使用子选择：abc@domain.com收到的所有邮件中没有来自同一域的其他收件人@ domain.com ??

我能找到的唯一方法是使用子选择：

select mail m, recipient r where m.pkm=r.pkm 
and (r.address='abc@domain.com')
and not exists (select * from mail ms, recipient rs where m.pkm=ms.pkm and ms.pkm=rs.pkm and rs.address<>'abc@domain.com' and rs.address like '%@domain.com')

Answer 1

select m.*, r1.* 
from mail m
inner join recipient r1 on m.pkm=r1.pkm
left join recipient r2 on m.pkm=r2.pkm and r2.address<>'abc@domain.com' and r2.address like '%@domain.com'
where r2.pkm is null
and r1.address='abc@domain.com'

Answer 2

我不确定这比你原来的更好！ - 它仍然有一个子选择 - 但允许域不是文字'domain.com'。

SELECT m.*
FROM mail m
INNER JOIN 
(
    SELECT DISTINCT pkm
    FROM recipient
    GROUP BY pkm, SUBSTRING(email, CHARINDEX('@', email) + 1, 1000)
    HAVING COUNT(SUBSTRING(email, CHARINDEX('@', email) + 1, 1000))  = 1
) r
ON m.pkm = r.pkm

hth，R

是否可以编写一个SQL查询，在没有子选择的情况下执行此操作？

2 个答案: